In a satellite communication system, subscribers can be distributed across a wide geographical area. Information transmitted from each of the subscribers is uplinked to a communication satellite where it is combined with the transmitted information from other subscribers and routed to another node of the communication system such as a ground receiving station. This information can represent analog voice, digitized voice or data, or a combination of voice and data. In a satellite communication system that is comprised of a plurality of satellites, the combined transmitted information can also be routed to another satellite through an intersatellite link. In satellite communication systems, a channelizer is useful in separating the information of a single subscriber from a combined stream of transmitted information. In such a system, the channelizer can be used in either a satellite, or a ground station.
In a communication system which is required to be lightweight and low power-consuming, an optical channelizer can be used to efficiently separate a stream of information from a single subscriber from a combined stream of information. Optical channelizers also convert the individual subscriber information channels to base band. After conversion to base band, the information can be extracted from the individual subscriber channel according to well-known techniques. An additional advantage that optical channelizers possess over other techniques of channelization and down conversion, is the capability to perform these functions on many inputs modulated over a large bandwidth.
In an optical channelizer, an optical signal is modulated and transmitted through a pair of columnar Bragg cells arranged side-by-side. The Bragg cells spatially disperse the wideband frequency information contained within the optical signal. The spatially dispersed frequency information is then transmitted through a time-domain transforming lens and projected onto a detector array. The detectors which comprise the array extract the channel information from the interference pattern through the use of well-known techniques. In a typical system, the output of each detector is then filtered to remove unwanted channel information from adjacent detectors. The additional channel information from adjacent detectors is referred to as inter-symbol interference. The filtering of the detector output to reduce the inter-symbol interference significantly increases the weight and power requirements for the optical channelizer system.
Inter-symbol interference at the detector output can also be reduced by electronically filtering the wideband information channel prior to applying the signal to the acousto-optic modulator. However, this implementation is costly and has the negative effect of distorting the wideband information channels. Additionally, this technique also adds significant weight to the optical channelizer system.
Therefore, what is needed, are a method and system for down converting and channelizing a wide band input signal and filtering each of the resulting channels.